Storage system for controlling assignment of storage area to virtual volume storing specific pattern data

ABSTRACT

A storage system comprises a storage medium including a plurality of physical storage areas. The storage system controls a host computer to recognize a logical volume having a plurality of virtual storage areas, reads the data from the physical storage area assigned to the virtual storage area of the logical volume, determines whether or not the read data includes only the specific pattern data, and cancels the assignment of the physical storage area to the virtual storage area if the read data includes only the specific pattern data.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.13/238,870, filed Sep. 21, 2011, which is a continuation application ofU.S. Ser. No. 12/292,604, filed Nov. 21, 2008, now U.S. Pat. No.8,793,461 and relates to and claims priority from Japanese PatentApplication No. 2008-256314, filed on Oct. 1, 2008, the entiredisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technology for managing a storagearea in a storage system as disclosed in the specification of thisapplication. More particularly, the invention relates to management ofassigning a real storage area to a virtual storage area.

2. Description of the Related Art

In a computer system using a computer and a storage system, the amountof data stored in the storage system generally tends to increase. Tocope with this increase, if a storage system having a sufficient datastorage capacity is introduced from the beginning, a high introductioncost arises. On the other hand, if the data storage capacity of thestorage system is expanded sequentially along with the increasing amountof data, a management cost for expansion arises. To reduce suchintroduction cost and management cost, a technology for the storagesystem to provide a virtual storage area to the computer was disclosed(e.g., refer to JP-A-2003-15915).

With this technology, the virtual storage area having sufficient datastorage capacity is defined, but the physical storage area (e.g.,storage area on a hard disk drive) is not assigned to all the virtualstorage area. Thereafter, physical storage areas are sequentiallyassigned to the virtual storage area in accordance with a data writerequest into the virtual storage area. Since the physical storage areais not assigned to the unused range of the defined virtual storage area,the physical storage area can be effectively used.

SUMMARY OF THE INVENTION

If receiving a data read request from the range of the virtual storagearea as above, to which the physical storage area is not assigned, thestorage system returns specific pattern data (e.g., consecutive “0”).Therefore, if the data is read from the entire virtual storage area andstored in a tape storage medium, the above specific pattern data isstored as the data read from the range to which the physical storagearea is not assigned, for example. Thereafter, if the data stored in thetape storage medium is restored in the virtual storage area, the abovespecific pattern data is written into the virtual storage area, so thatthe physical storage area is assigned to all the virtual storage area.As a result, the physical storage area cannot be effectively used.

The typical invention as disclosed in this application provides astorage system for storing the data written by a host computer, thestorage system comprising a storage medium including a plurality ofphysical storage areas, and a controller for controlling the write ofthe data into the storage medium and the read of the data from thestorage medium, characterized in that the controller controls the hostcomputer to recognize a first logical volume, a storage area space ofthe first logical volume includes a plurality of address ranges, and thecontroller holds information for managing the assignment of eachphysical storage area to each address range, determines whether or notthe physical storage area is assigned to the address range specified bya received data write request, if the data write request for any of theaddress ranges of the first logical volume is received, assigns thephysical storage area not yet assigned to any of the address ranges tothe specified address range if the physical storage area is not assignedto the specified address range, writes write requested data in the datawrite request into the physical storage area assigned to the specifiedaddress range, reads the data from the physical storage area assigned tothe address range of the first logical volume if a predeterminedcondition is satisfied, determines whether or not the read data includesthe data of a predetermined pattern only, cancels the assignment of thephysical storage area to the address range if the read data includes thedata of the predetermined pattern only, determines whether or not thephysical storage area is assigned to the address range specified by adata read request if the data read request for any of the address rangesof the first logical volume is received, sends the read data to a senderof the data read request by reading the data from the physical storagearea assigned to the specified address range if the physical storagearea is assigned to the specified address range, and sends the data ofthe predetermined pattern to the sender of the data read request if thephysical storage area is not assigned to the specified address range.

With one embodiment of the invention, it is possible to make effectiveuse of the physical storage area by preventing the physical storage areafrom being assigned to the range into which specific pattern data iswritten.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a computer systemaccording to a first embodiment of the present invention.

FIG. 2 is an explanatory view of a logical volume managed by a storagesystem according to the first embodiment of the invention.

FIG. 3 is an explanatory view for assigning the physical storage area tothe virtual volume according to the first embodiment of the invention.

FIG. 4 is an explanatory view of an assignment management tableaccording to the first embodiment of the invention.

FIG. 5 is an explanatory view of a pair management table according tothe first embodiment of the invention.

FIG. 6 is a flowchart showing a data write process according to thefirst embodiment of the invention.

FIG. 7 is a flowchart showing a data read process according to the firstembodiment of the invention.

FIG. 8 is a flowchart showing a pool JOB according to the firstembodiment of the invention.

FIG. 9 is a flowchart showing a page discard determination processaccording to the first embodiment of the invention.

FIG. 10 is an explanatory view for making the comparison of dataaccording to the first embodiment of the invention.

FIG. 11 is a flowchart showing a page discard process according to thefirst embodiment of the invention.

FIG. 12 is a flowchart showing a data write process according to asecond embodiment of the invention.

FIG. 13 is a flowchart showing a first example of data copy between thelogical volumes according to the second embodiment of the invention.

FIG. 14 is a flowchart showing a second example of data copy between thelogical volumes according to the second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First of all, a first embodiment of the present invention will bedescribed below in detail using the drawings.

FIG. 1 is a block diagram showing the configuration of a computer systemaccording to the first embodiment of the invention.

The computer system of this embodiment comprises a storage system 100A,a storage system 100B, a tape library 120, a host computer 130 and anetwork 140 for interconnecting them.

The storage system 100A stores the data written by the host computer130. More specifically, the storage system 100A comprises the diskdrives 110A to 110C and a controller 101.

Each of the disk drives 110A to 110C is a storage device comprising astorage medium for storing the data written by the host computer 130. Inthe following, in giving the explanation common to the disk drives 110Ato 110C, they are generically called a disk drive 110. Though three diskdrives 110 are shown in FIG. 1, the storage system 100A may comprise anynumber of disk drives 110. A plurality of disk drives 110 may constitutea RAID (Redundant Array of Inexpensive Disks).

The disk drive 110 of this embodiment is a hard disk drive having amagnetic disk as the storage medium, but may be replaced with any typeof storage device. For example, the disk drive 110 may be replaced witha non-volatile semiconductor storage device such as a flash memory.

The controller 101 controls the write of the data into the disk drive110 and the read of the data from the disk drive 110. The controller 101comprises a channel adaptor 102, a shared memory 103, a disk adaptor104, a cache memory 105 and an internal network 116 for interconnectingthem.

The channel adaptor 102 comprises a CPU 106, a local memory 107, a port108 and a port 109.

The CPU 106 is a processor for executing a program stored in the localmemory 107.

The local memory 107 stores the program executed by the CPU 106 and thedata referred to by the CPU 106. The local memory 107 of this embodimentstores at least an I/O control program 112 and an assignment managementprogram 113. These will be described later in detail. In the followingexplanation, a process performed by the I/O control program 112 or theassignment management program 113 is actually performed on the CPU 106that executes the program.

The port 108 is connected to the network 140, and used for communicationwith the host computer 130. The port 109 is connected to the internalnetwork 116 and used for communication with the disk adaptor 104.

The shared memory 103 stores control information and so on referred toby the channel adaptor 102 or the like. The shared memory 103 of thisembodiment stores at least an assignment management table 114 and a pairmanagement table 115. These will be described later in detail.

The disk adaptor 104 is connected to the disk drive 110, and controlsthe write and read of the data into and from the disk drive 110 underthe control of the channel adaptor 102.

The cache memory 105 temporarily stores the data written into the diskdrive 110 and the data read from the disk drive 110.

The storage system 100A may comprise a plurality of channel adaptors102, a plurality of shared memories 103, a plurality of disk adaptors104 and a plurality of cache memories 105.

The internal network 116 is realized by a bus or a fabric switch, forexample.

The controller 101 manages the physical storage areas realized by thestorage medium of the disk drive 110 as a plurality of logical volumes111. Each of the logical volumes 111A and 111B as shown in FIG. 1 is oneof the plurality of logical volumes 111. The controller 101 can manageany number of logical volumes 111. The logical volume 111 will bedescribed later in detail (see FIG. 2).

The configuration of the storage system 100B is the same as the storagesystem 100A, and not illustrated and described here.

In the following, in giving the explanation common to the storagesystems 100A and 100B, they are generically called a storage system 100.

The tape library 120 is mainly used to back up the data stored in thestorage system 100. The tape library 120 comprises a tape drive 121 andone or more tape storage media 122.

Each tape storage medium 122 may be one volume of tape stored in acartridge. Each of the tape storage media 122A and 122B as shown in FIG.1 is one of the plurality of tape storage media 122.

The tape drive 121 mounts the tape storage medium 122 and performs thewrite of the data into the tape storage medium 122 and the read of thedata from the tape storage medium 122. For example, the tape drive 121may write the duplicate of the data stored in the logical volume 111into one or more tape storage media 122.

The host computer 130 comprises a CPU 131, a memory 132 and an interface133 which are interconnected.

The CPU 131 is a processor for executing a program stored in the memory132.

The memory 132 stores the program executed by the CPU 131 and the datareferred to by the CPU 131. The memory 132 of this embodiment stores atleast an application program 134.

The interface 133 is connected to the network 140 and performs thecommunication with the storage system 100.

The CPU 131 executes the application program 134, and sends a data writerequest or data read request into or from the logical volume 111 via theinterface 133 to the storage system 100, as needed.

The network 140 may be any type. Typically, the network 140 is aso-called storage area network (SAN) to which a fibre channel protocolis applied. In this case, the network 140 may comprise a fibre channelswitch (not shown).

FIG. 2 is an explanatory view of the logical volume 111 managed by thestorage system 100 according to the first embodiment of the invention.

The computer system as shown in FIG. 2 corresponds to that as shown inFIG. 1, but the hardware configuration unnecessary for the explanationof the logical volume 111 is not illustrated.

The controller 101 in the storage system 100 of this embodiment managesthree types of logical volumes 111, namely, a virtual volume 201, a realvolume 202 and a pool volume 203. More specifically, the storage system100A manages a virtual volume 201A, a virtual volume 201B, a real volume202A, a pool volume 203A and a pool volume 203B in an example of FIG. 2.The storage system 100B manages a virtual volume 201C, a virtual volume201D, a real volume 202B, a pool volume 203C and a pool volume 203D.

In the following, in giving the explanation common to the virtualvolumes 201A to 201D, they are generically called a virtual volume 201.Similarly, the real volumes 202A and 202B are generically called a realvolume 202, and the pool volumes 203A to 203D are generically called apool volume 203. The pools 204A and 204B as will be described later arealso generically called a pool 204.

The controller 101 provides a storage area space of each real volume 202to the host computer 130. The host computer 130 recognizes each realvolume 202 as one storage device, and issues a data write request and adata read request for each real volume 202.

The physical storage area of the disk drive 110 is assigned to all thestorage area space of each real volume 202. The controller 101 receivinga data write request or data read request for the real volume 202performs the write or read of the data into or from the physical storagearea assigned to the storage area corresponding to the addressdesignated as access target by the received request.

Similarly, the controller 101 provides a storage area space of eachvirtual volume 201 to the host computer 130. The host computer 130recognizes each virtual volume 201 as one storage device, and issues adata write request and a data read request for each virtual volume 201.

However, the physical storage area of the disk drive 110 may not beassigned to all the storage area space of each virtual volume 201 insome cases. The controller 101 can control the assignment of thephysical storage area to any address range of the storage area space foreach virtual volume 201.

Usually, at the point in time when the virtual volume 201 is created,the physical storage area is not assigned to any address range of thestorage area space for the virtual volume 201. Thereafter, thecontroller 101 receiving a data write request at any address of thevirtual volume 201 assigns the physical storage area to the addressrange including the address of the write target and stores the data inthe assigned physical storage area.

The physical storage area is not directly assigned to the address rangeof the virtual volume 201, but the storage area space (more specificallythe address range) of the pool volume 203 is assigned as will bedescribed later. Thereby, the assignment of the physical storage area tothe virtual volume 201 is implemented.

A process for writing or reading the data into or from the virtualvolume 201 will be described later.

The pool volume 203 is the same logical volume 111 as the real volume202. That is, the physical storage area of the disk drive 110 isassigned to all the storage area space of the pool volume 203.

However, the storage area space of the pool volume 203, unlike the realvolume 202, is not directly provided to the host computer. The storagearea space of the pool volume 203 is assigned to the storage area spaceof the virtual volume 201, as needed.

In this embodiment, one or more pool volumes 203 make up one pool 204.The pool 204 is associated with the virtual volume 201 as the supplierof the physical storage area. In the example of FIG. 2, the pool 204A iscomposed of a plurality of pool volumes 203 including the pool volumes203A and 203B. The pool 204A is associated with the virtual volumes 201Aand 201B.

In this example, when it is required to assign the physical storage areato the virtual volume 201A, the storage area space of any pool volume203 (e.g., pool volume 203A) belonging to the pool 204A associated withthe virtual volume 201A is assigned. When it is required to assign thephysical storage area to the virtual volume 201B, the storage area spaceof any pool volume 203 (e.g., pool volume 203A) belonging to the pool204A associated with the virtual volume 201B is assigned.

Similarly, the pool 204B is composed of a plurality of pool volumes 203including the pool volumes 203C and 203D. The pool 204B is associatedwith the virtual volumes 201C and 201D.

FIG. 3 is an explanatory view for assigning the physical storage area tothe virtual volume 201 according to the first embodiment of theinvention.

For the sake of simplification of the explanation, FIG. 3 shows anexample in which the pool 204A is associated with the virtual volume201A and the pool 204A includes the pool volume 203A only.

The assignment of the physical storage area to the storage area space ofthe virtual volume 201A is managed for each address range ofpredetermined size (e.g., a range of block address as will be describedlater). The address range of predetermined size is called a page. Inother words, the page of the virtual volume 201 is the virtual storagearea of predetermined size.

In the example of FIG. 3, the page 301C of the pool volume 203A isassigned to the page 301A of the virtual volume 201A. This assignment ismanaged by the assignment management table 114.

The physical storage area is assigned to all the pages of the poolvolume 203A, as already described. Therefore, for example, if a datawrite request for any address within the page 301A is issued, the datais written into the physical storage area assigned to the page 301C. Inthis way, the physical storage area assigned to the page 301C can beregarded as being assigned via the assignment management table 114 tothe page 301A. In other words, since the physical storage area isassigned to all the pages of the pool volume 203A, each page of the poolvolume 203A can be regarded as the physical storage area.

On the other hand, no page of the pool volume 203A is assigned to thepage 301B of the virtual volume 201A.

Specific pattern data is stored in a predetermined address range 303(more correctly the physical storage area assigned to the address range303) of the pool volume 203A. This specific pattern is predetermined.For example, the specific pattern data may be the data composed of “0”only. The predetermined address range 303 is not assigned to any pagewithin the virtual volume 201A.

Each page may include a predetermined number of blocks. Herein, a blockis the minimum unit of area designated as the data write target (dataread object) by the data write request (or data read request). Eachblock has a fixed size (e.g., 512 bytes), and is identified by the blockaddress. In the example of FIG. 3, the block 302C included in the page301C is assigned to the block 302A included in the page 301A. In thiscase, the data written into the block 302A is actually stored in thephysical storage area assigned to the block 302C.

On the other hand, the block 302B is included in the page 301B in theexample of FIG. 3. However, since the page of the pool volume 203A isnot assigned to the page 301B, the block of the pool volume 203A is notassigned to the block 302B.

FIG. 4 is an explanatory view of the assignment management table 114according to the first embodiment of the invention.

The assignment management table 114 is stored in the shared memory 103,and includes information for managing the assignment of the physicalstorage area to the virtual volume 201. More specifically, theassignment management table 114 includes a virtual page 401, a real page402 and a discard mark 403.

The virtual page 401 is information for identifying each page of thevirtual volume 201. For example, the virtual page 401 may be the initialaddress of each page in the virtual volume 201.

The real page 402 is information for identifying the page of the poolvolume 203 assigned to each page of the virtual volume 201. The realpage 402, like the virtual page 401, may be the initial address of eachpage in the pool volume 203. If the page of the pool volume 203 is notassigned to a certain page of the virtual volume 201, an invalid valueis registered as the real page 402 corresponding to the page of thevirtual volume 201.

The discard mark 403 is a flag indicating discarding a page of thevirtual volume 201 (i.e., deleting allocation of page of the pool volume203 for page of the virtual volume 201). A page discard determinationprocess and a page discard process using the discard mark 403 areexplained in detail later.

In the example of FIG. 4, “0x0000” and “0x0000” are registered as thevirtual page 401 and the real page 402 in the first entry of theassignment management table 114. On the other hand, “0x5000” and theinvalid value are registered as the virtual page 401 and the real page402 in the second entry. This reveals that the pages (e.g., page 301C inFIG. 3) corresponding to the range from the block address “0x0000” to“0x4FFF” in the pool volume 203A are assigned to the pages (e.g., page301A in FIG. 3) corresponding to the range from the block address“0x0000” to “0x4FFF” in the virtual volume 201A, and the pages of thepool volume 203A are not assigned to the pages (e.g., page 301B in FIG.3) corresponding to the range from the block address “0x5000” to“0x9FFF” in the virtual volume 201A.

FIG. 5 is an explanatory view of a pair management table 115 accordingto the first embodiment of the invention.

The pair management table 115 is stored in the shared memory 103, andincludes information for managing a copy pair. Herein, the copy pairwill be described below.

The copy pair is a set (pair) of the logical volume 111 and the logicalvolume 111 (i.e., copy target) for storing the duplicate of the datastored in the logical volume 111. For example, to back up the logicalvolume 111, the copy pair is created. The copy pair may be composed oftwo logical volumes 111 within one storage system 100, or two logicalvolumes 111 included in different storage systems 100.

Each of the logical volume 111 of copy source and the logical volume 111of copy target may be the virtual volume 201 or the real volume 202. Inthe following, the logical volume 111 of copy source is called a primaryvolume and the logical volume 111 of copy target is called a secondaryvolume.

When the copy pair is newly created, all the data stored in the primaryvolume is read, and all the read data is written into the secondaryvolume. Thereafter, if the data of the primary volume is updated, theupdate is reflected to the secondary volume. Thereby, the consistencybetween the data stored in the primary volume and the data stored in thesecondary volume is maintained.

Conversely, the data stored in the secondary volume may be copied to theprimary volume. For example, if the data stored in the primary volume islost due to a failure or malfunction, the data stored in the secondaryvolume can be copied to the primary volume to restore the data.

If the copy pair is created by two logical volumes 111, the informationfor managing the copy pair (in other words, the information forassociating the two logical volumes 111) is registered in the pairmanagement table 115.

The pair management table 115 includes a device ID of primary volume501, a volume ID of primary volume 502, a type of primary volume 503, adevice ID of secondary volume 504, a volume ID of secondary volume 505,and a type of secondary volume 506.

The device ID of primary volume 501 is an identifier of the storagesystem that stores the primary volume belonging to the copy pair.

The volume ID of primary volume 502 is an identifier of the primaryvolume belonging to the copy pair.

The type of primary volume 503 indicates which of the virtual volume 201and the real volume 202 the primary volume belonging to the copy pairis.

The device ID of secondary volume 504 is an identifier of the storagesystem that stores the secondary volume belonging to the copy pair.

The volume ID of secondary volume 505 is an identifier of the secondaryvolume belonging to the copy pair.

The type of secondary volume 506 indicates which of the virtual volume201 and the real volume 202 the secondary volume belonging to the copypair is.

In the example of FIG. 5, “ST01”, “VOL02”, “real”, “ST02”, “VOL12” and“virtual” are stored as the device ID of primary volume 501, the volumeID of primary volume 502, the type of primary volume 503, the device IDof secondary volume 504, the volume ID of secondary volume 505, and thetype of secondary volume 506 in the second entry of the pair managementtable 115. For example, when the identifier of the storage system 100Ais “ST01”, the identifier of the storage system 100B is “ST02”, theidentifier of the real volume 202A is “VOL02”, and the identifier of thevirtual volume 201D is “VOL12”, the second entry reveals that the copypair in which the real volume 202A is the primary volume and the virtualvolume 201D is the secondary volume is created.

Next, the write of the data into the virtual volume 201 and the read ofthe data from the virtual volume 201 will be described below.

FIG. 6 is a flowchart showing a data write process according to thefirst embodiment of the invention.

More specifically, FIG. 6 shows the process to be performed when the I/Ocontrol program 112 receives a data write request with the virtualvolume 201 designated as the write target.

At first, the I/O control program 112 receives the data write request(step 601). This data write request includes the data to be written andthe information for designating the address of the write target of thedata.

This data write request may be sent from the host computer 130, by apair control program (not shown) of any storage system 100 to performthe copy of data in the copy pair, or by the tape library 120 or backupcontrol device (not shown) to restore the data from the tape storagemedium.

Next, the I/O control program 112 determines whether or not the physicalstorage area is assigned to the page including the address of the writetarget (step 602). More specifically, the I/O control program 112determines whether or not the valid value (i.e., address of any page inthe pool volume 203) is registered in the real page 402 corresponding tothe page including the address of the write target by referring to theassignment management table 114.

If it is determined at the step 602 that the invalid value is registeredin the real page 402 corresponding to the page including the address ofthe write target, the physical storage area is not assigned to the pageincluding the address of the write target. In this case, the I/O controlprogram 112 assigns the physical storage area not yet assigned to anypage to the page including the address of the write target (step 603).

More specifically, the I/O control program 112 selects the page not yetassigned to any page of the virtual volume from among the pages of thepool volume 203 corresponding to the virtual volume 201 of the writetarget and registers the address of the selected page in the real page402 corresponding to the page including the address of the write target.

An assignment process at the step 603 may be performed by the assignmentmanagement program 113 receiving an instruction from the I/O controlprogram 112.

Next, the I/O control program 112 writes the data at the address of thewrite target (step 604). More specifically, the I/O control program 112specifies the physical storage area assigned to the address of the writetarget by referring to the assignment management table 114 and writesthe data in the specified physical storage area.

On the other hand, if it is determined at the step 602 that the validvalue is registered in the real page 402 corresponding to the pageincluding the address of the write target, the physical storage area isassigned to the page including the address of the write target. In thiscase, the I/O control program 112 does not perform the step 603 andperforms the step 604.

With the above, the data write process is ended.

In the above way, the physical storage area can be effectively used bysuspending the assignment of the physical storage area to the logicalvolume until it is actually used (i.e., the data is written). Such atechnique for dynamically assigning the physical storage area inaccordance with the data write request is called an Allocation on Use(AoU).

Herein, referring to FIGS. 3 and 4, a specific example of the data writeprocess will be described below.

For example, if the block 302A is designated as the write target, theI/O control program 112 determines that the page 301C of the pool volume203A is assigned (i.e., the physical storage area is assigned) to thepage 301A including the block 302A by referring to the assignmentmanagement table 114 (step 602). This determination is made based on thefact that the address of the designated block 302A is included in therange from “0x0000” to “0x4FFF”.

In this case, the I/O control program. 112 writes the data into theblock 302C assigned to the block 302A (more correctly the physicalstorage area assigned to the block 302C) (step 604).

On the other hand, in the above example, if the real page 402corresponding to the value “0x0000” of the virtual page 401 is theinvalid value, the page of the pool volume 203A is not assigned to thepage 301A including the block 302A. In this case, the I/O controlprogram 112 assigns the page (e.g., page 301C) of the pool volume 203Ato the page 301A. More specifically, the initial address “0x0000” of thepage 301C is newly registered as the real page 402 corresponding to thevalue “0x0000” of the virtual page 401, for example, as shown in FIG. 4.Thereafter, the I/O control program 112 writes the data into the block302C assigned to the block 302A (step 604).

FIG. 7 is a flowchart showing a data read process according to the firstembodiment of the invention.

More specifically, FIG. 7 shows the process to be performed when the I/Ocontrol program 112 receives a data read request (i.e., request forreading the data from the virtual volume 201) with the virtual volume201 designated as the read object.

At first, the I/O control program 112 receives a data read request (step701). This data read request includes the information for designatingthe address of the read object of data (i.e., information indicating theaddress of the stored data to be read).

This data read request may be sent from the host computer 130, or by thepair control program (not shown) to perform the copy of the data in thecopy pair.

Next, the I/O control program 112 determines whether or not the physicalstorage area is assigned to the page including the address of readobject (step 702). This determination is performed in the same way as atthe step 602 in FIG. 6.

If it is determined at the step 702 that the physical storage area isassigned to the page including the address of the read object, the I/Ocontrol program 112 reads the data from the address of read object (step703). More specifically, the I/O control program 112 specifies thephysical storage area assigned to the address of the read object byreferring to the assignment management table 114, and reads the datafrom the physical storage area.

On the other hand, if it is determined at the step 702 that the physicalstorage area is not assigned to the page including the address of theread object, the I/O control program 112 reads the specific pattern datastored in a predetermined address range (step 704).

Then, the I/O control program 112 sends the data read at the step 703 orthe step 704 as a response to the data read request to the requestsource (step 705).

Herein, referring to FIGS. 3 and 4, a specific example of the data readprocess will be described below.

For example, if the block 302A is designated as the read object, the I/Ocontrol program 112 determines that the page 301C of the pool volume203A is assigned (i.e., the physical storage area is assigned) to thepage 301A including the block 302A by referring to the assignmentmanagement table 114 (step 702).

In this case, the I/O control program 112 reads the data stored in theblock 302C assigned to the block 302A (more correctly the physicalstorage area assigned to the block 302C) (step 703), and sends the datato the request source (step 705).

On the other hand, for example, if the block 302B is designated as theread object, the I/O control program 112 determines that the page of thepool volume 203A is not assigned (i.e., the physical storage area is notassigned) to the page 301B including the block 302B by referring to theassignment management table 114 (step 702).

In this case, the I/O control program 112 reads the specific patterndata (e.g., data composed of consecutive “0” only) stored in the addressrange 303 (step 704), and sends the data to the request source (step705).

Herein, the problems to be solved by the invention and the forms forsolving the problems will be outlined below by referring to the aboveexample.

For example, a process for writing the duplicate of the data stored inthe virtual volume 201 into the tape storage medium. 122 for backup maybe performed. In this case, the data stored in the virtual volume 201 isread as shown in FIG. 7, and written into the tape storage medium 122.At this time, the specific pattern data is sent in response to a readrequest for the page to which the physical storage area is not assignedamong the pages of the virtual volume 201. Therefore, the specificpattern data sent in response in the above way is stored in the tapestorage medium 122, as the data read from the page to which the physicalstorage area is not assigned.

Thereafter, if it is desired that the data stored in the tape storagemedium 122 is restored in the virtual volume 201, the data stored in thetape storage medium 122 is read and written into the virtual volume 201.At this time, the specific pattern data stored in the tape storagemedium 122 is all read and written into the virtual volume 201. At thistime, since the process for writing the read specific pattern data isperformed, the physical storage area for storing the specific patterndata is assigned to the page of the virtual volume 201 and the specificpattern data is written, as shown in FIG. 6.

In this way, the physical storage area is assigned by restore to thepage to which the physical storage area is not assigned before restore.Thereby, the feature of the AoU technique to make effective use of thephysical storage area is lost.

The above problem also occurs on the data copy between the copy pair.

For example, when the copy pair in which the primary volume is thevirtual volume 201 and the secondary volume is the real volume 202 iscreated, all the data stored in the virtual volume 201 is firstly readand stored in the real volume 202. At this time, the specific patterndata is stored in the real volume 202, as the data read from the page towhich the physical storage area is not assigned, in the same way as inthe above case of the tape storage medium.

Thereafter, if the data of the secondary volume is restored to theprimary volume, the specific pattern data stored in the real volume 202is all read and written into the virtual volume 201, in the same way asin the above case of the tape storage medium. At this time, the physicalstorage area for storing the specific pattern data is assigned to thepage of the virtual volume 201.

To avoid such a problem, in this embodiment, the specific pattern dataonce written is detected, whereby the assignment of the physical storagearea to the page storing only the specific pattern data is canceled.This process will be described below.

FIG. 8 is a flowchart showing a pool JOB according to the firstembodiment of the invention.

The pool JOB is performed by the assignment management program 113 ofeach storage system 100.

The assignment management program 113 firstly determines whether or nota predetermined condition is satisfied (step 801). For example, theassignment management program 113 may determine that the predeterminedcondition is satisfied for each pool 204, if the percentage of the totalamount of the page already assigned to the virtual volume 201 to thetotal storage capacity of the pool 204 exceeds a predeterminedthreshold.

If it is determined at the step 801 that the predetermined condition isnot satisfied, the step 801 is repeated until the predeterminedcondition is satisfied.

If it is determined at the step 801 that the predetermined condition issatisfied, the assignment management program 113 selects one of thevirtual volumes 201 associated with the pool 204, for which thepredetermined condition is satisfied (step 802).

Then, the assignment management program 113 performs a page discarddetermination process for the selected virtual volume 201 (step 803).The page discard determination process will be described later (see FIG.9).

Then, the assignment management program 113 performs a page discardprocess for the selected virtual volume 201 (step 804). The page discardprocess will be described later (see FIG. 11).

Next, the assignment management program 113 determines whether or notthe virtual volume 201 selected at the step 801 is the last, in otherwords, the steps 803 and 804 are performed for all the virtual volumes201 associated with the pool 204 for which it is determined that thepredetermined condition is satisfied at the step 801 (step 805).

If it is determined at the step 805 that the virtual volume 201 selectedat the step 801 is not the last, the process returns to the step 802. Inthis case, at the step 802, the assignment management program 113selects one of the remaining virtual volumes 201. The assignmentmanagement program 113 repeats the steps 802 to 805 until the pagediscard determination process (step 803) and the page discard process(step 804) are performed for all the virtual volumes 201 associated withthe pool 204 for which it is determined that the predetermined conditionis satisfied at the step 801.

If it is determined at the step 805 that the virtual volume 201 selectedat the step 801 is the last, the assignment management program 113 endsthe pool JOB.

Herein, the variation of the determination at the step 801 will bedescribed below. Though in the above example it is determined that thepredetermined condition is satisfied if the percentage of the totalamount of the page assigned to the virtual volume 201 exceeds thepredetermined threshold, the determination may be made by other methods.

For example, if the percentage of the total amount of the page with thephysical storage area already assigned to the total capacity defined inthe certain virtual volume 201 exceeds the predetermined threshold, itmay be determined that the predetermined condition is satisfied. In thiscase, the virtual volume 201 for which the above percentage exceeds thepredetermined threshold is selected at the step 802.

Or when a predetermined timing arrives, it may be determined that thepredetermined condition is satisfied. More specifically, when apredetermined time passes since the previous pool JOB is executed, orwhen a predetermined time arrives, it may be determined that thepredetermined condition is satisfied for all the pools 204 within thestorage system 100. In this case, the steps 802 to 805 are repeatedlyperformed for all the virtual volumes unless they are not associatedwith any pool 204.

The above predetermined timing may be the timing when a pooloptimization process is performed. The pool optimization process is theprocess for randomizing the correspondence between the unassigned pageof the virtual volume 201 and the unassigned page within the pool 204.

Or the user or manager of the storage system 100 may instruct the poolJOB to be executed by designating the pool 204 or the virtual volume201. More specifically, the user or manager may send a pool JOBexecution instruction including the designation of the pool 204 orvirtual volume 201 to the storage system 100, using the host computer130, for example. The assignment management program 113 of the storagesystem receiving this instruction determines that the predeterminedcondition is satisfied for the designated pool 204 or virtual volume 201(step 801).

Or if the copy from the real volume 202 to the virtual volume 201 isperformed in the copy pair, it may be determined that the predeterminedcondition is satisfied. This is because there are some cases where thephysical storage area is assigned to store the specific pattern data bythe copy from the real volume 202 to the virtual volume 201, as alreadydescribed.

More specifically, for example, the assignment management program 113may determine at the step 801 whether or not the copy from the realvolume 202 to the virtual volume 201 is performed, and may furtherdetermine whether or not the copy source is the real volume 202 and thecopy target is the virtual volume 201 if it is determined that the copyis performed. It is determined whether or not each logical volumebelongs to the copy pair, and if so, the attribute of the copy pair canbe known by referring to the pair management table 115.

As a result of the above determination, if it is determined that thecopy source is the real volume 202 and the copy target is the virtualvolume 201, the virtual volume 203 of the copy target is selected at thestep 802.

Or if the data read from the tape storage medium is copied to thevirtual volume 201, it may be determined that the predeterminedcondition is satisfied. This is because there are some cases where thephysical storage area is assigned to store the specific pattern data bythe copy from the tape storage medium to the virtual volume 201, asalready described. In this case, the virtual volume 203 of the copytarget is selected at the step 802.

FIG. 9 is a flowchart showing the page discard determination processaccording to the first embodiment of the invention.

The page discard process as shown in FIG. 9 is performed at the step 803of the pool JOB as shown in FIG. 8.

At first, the assignment management program 113 validates the value ofthe discard mark 403 corresponding to the page to which the physicalstorage area is already assigned among all the pages of the virtualvolume 201 selected at the step 802 (step 901). For example, the discardmark 403 is valid when the value is “1” and invalid when the value is“0”, or may be reversely represented.

Next, the assignment management program 113 selects one of the pages ofthe selected virtual volume 201 (step 902). At the step 902 that isperformed for the first time after the start of the page discarddetermination process, the first page of the virtual volume 201 may beselected.

Next, the assignment management program 113 determines whether or notthe value of the discard mark 403 corresponding to the selected page isvalid (step 903).

If it is determined at the step 903 that the value of the discard mark403 corresponding to the selected page is invalid, the physical storagearea is not assigned to the page, or the assignment of the physicalstorage area to the page must not be canceled. Therefore, the assignmentmanagement program 113 does not perform the process following the step904 (i.e., the process for canceling the assignment of the physicalstorage area to the selected page) and returns to the step 902.

On the other hand, if it is determined at the step 903 that the value ofthe discard mark 403 corresponding to the selected page is valid, theassignment management program 113 selects one of the slots in theselected page, and stages the data of the slot (step 904). For example,at the step 904 that is performed for the first time after the page isselected, the first slot of the selected page may be selected.

The slot is a management unit of data within the page. One page isdivided into a predetermined number of slots. A comparison between thedata stored in the page and the specific pattern data is made for eachslot (see FIG. 10).

The staging of the data in the slot means reading the data in the slotand temporarily storing it in the memory. The data read from the slotmay be stored in the local memory 107, the shared memory 103 or thecache memory 105.

Next, the assignment management program 113 compares the data read fromthe slot and the specific pattern data, and determines whether or notthey are matched (step 905). This comparison may be made by any method.This comparison will be described later in detail (see FIG. 10).

If it is determined at the step 905 that the data read from the slot andthe specific pattern data are unmatched, the data other than thespecific pattern data is stored in the physical storage area assigned tothe selected page. That is, the assignment cannot be canceled.Therefore, the assignment management program 113 changes the value ofthe discard mark 403 corresponding to the selected page to the invalidvalue (step 906).

Next, the assignment management program 113 determines whether or notthe selected slot is the last slot of the selected page (step 907).

If it is determined at the step 907 that the selected slot is not thelast slot of the selected page, there is a slot which is not comparedwith the specific pattern data among the slots of the selected page.Therefore, the process returns to the step 904. At the step 904, one ofthe unselected slots (e.g., the next slot to the previously selectedslot) is selected.

On the other hand, if it is determined at the step 907 that the selectedslot is the last slot of the selected page, the comparison between allthe slots within the selected page (in other words, all the data) andthe specific pattern data is ended. In this case, the assignmentmanagement program 113 determines whether or not the selected page isthe last page within the selected virtual volume 201 (step 908).

If it is determined at the step 908 that the selected page is not thelast page within the selected virtual volume 201, there is a page forwhich it is not determined whether or not the assignment of the physicalstorage area is canceled among the pages within the selected virtualvolume 201. Therefore, the process returns to the step 902. At the step902, one of the unselected pages (e.g., the next page to the previouslyselected page) is selected.

If it is determined at the step 908 that the selected page is the lastpage within the selected virtual volume 201, it has been determinedwhether or not the assignment of the physical storage area is canceledfor all the pages within the selected virtual volume 201. In this case,the assignment management program 113 determines whether or not a dataI/O request (i.e., data write request or data read request) for any pagewithin the virtual volume 201 is performed after the step 901 for thecurrently selected virtual volume 201 (step 909).

If it is determined at the step 909 that the data write request isperformed, there is a high possibility that data other than the specificpattern data is written into the page in accordance with the data writerequest. On the other hand, if it is determined that the data readrequest is performed, there is a high possibility that the data writerequest for the page from which the data is read is performedimmediately after the read. This is because an operating system (OS)designed to necessarily perform the data read request for the area ofthe write target immediately before the data write request is performedoperates on the host computer 130. That is, there is a possibility thatthe data write request is performed immediately after the data readrequest is performed, and the data other than the specific pattern datais written into the page.

Accordingly, to prevent the cancellation of assignment of the physicalstorage area storing the data other than the specific pattern data tothe page, it is demanded that the assignment of the physical storagearea is not canceled for the page for which the data I/O request isperformed.

Therefore, if it is determined at the step 909 that the data I/O requestis performed, the assignment management program 113 changes the value ofthe discard mark 403 corresponding to the page subjected to the data I/Orequest to the invalid value (step 910).

On the other hand, if it is determined at the step 909 that the data I/Orequest is not performed, the assignment management program 113 does notperform the step 910.

In the example of FIG. 9, the steps 909 and 910 are performed after thestep 908. However, actually, it is desirable that the assignmentmanagement program 113 monitors the presence or absence of performingthe data I/O request at any time during the period from the start of thepage discard determination process until the end of the page discardprocess, and changes the discard mark 403 of the page subjected to therequest to the invalid value, when the data I/O request is performed.

With the above, the assignment management program 113 ends the pagediscard determination process.

FIG. 10 is an explanatory view for making the comparison of dataaccording to the first embodiment of the invention.

FIG. 10 shows the comparison of data in the virtual volume 201A as anexample, but the comparison of data is similarly made in other virtualvolumes 201.

The virtual volume 201A includes a plurality of pages of predeterminedsize, for example, page 301A and page 301B, as already described withreference to FIG. 3. Each page includes a plurality of slots ofpredetermined size. For example, the page 301A includes the slots 1001Ato 1001C.

For example, one page may include 168 slots, and one slot may include512 blocks (i.e., 256 kilobytes), but these values are a few examplesand any other values may be set.

A comparison work slot 1002 is prepared for the memory (e.g., localmemory 107) to store the specific pattern data. For example, the datastored in a predetermined address range 303 may be copied to thecomparison work slot 1002.

A comparator 1003 compares the data of each slot and the data of thecomparison work slot 1002 to determine whether or not they are the same.The comparator 1003 may be realized by dedicated hardware, or bysoftware.

For example, the data of the slot 1001A is firstly copied to the memory(step 904). The comparator 1003 compares the data of the slot 1001A andthe specific pattern data stored in the comparison work slot 1002 todetermine whether or not they are the same (step 905). If they are thesame, the next slot 1001B is copied to the memory and the above processis repeated.

For example, if the data of the slot 1001B and the specific pattern datastored in the comparison work slot 1002 are not the same, the value ofthe discard mark 403 corresponding to the page 301A is changed to theinvalid value. And the next page 301B is selected without making theabove comparison for the remaining slots (i.e., the slots following theslot 1001C) of the page 301A.

FIG. 11 is a flowchart showing the page discard process according to thefirst embodiment of the invention.

The page discard process as shown in FIG. 11 is performed at the step804 of the pool JOB as shown in FIG. 8.

At first, the assignment management program 113 acquires a resource lock(step 1101). This is a process for prohibiting the assignment of thephysical storage area to the page through another process than the pagediscard process being performed currently. That is, the assignment ofthe physical storage area to the page and its cancellation areexclusively controlled by acquiring the resource lock.

Then, the assignment management program 113 selects one of the pages inthe selected virtual volume 201 (step 1102). At the step 1102 that isperformed for the first time after the start of performing the pagediscard process, the first page of the virtual volume 201 may beselected.

Then, the assignment management program 113 determines whether or notthe value of the discard mark 403 corresponding to the page selected atthe step 1102 is valid (step 1103).

If it is determined at the step 1103 that the value of the discard mark403 corresponding to the selected page is valid, the specific patterndata only is stored in the selected page. In this case, the assignmentmanagement program 113 cancels the assignment of the physical storagearea to the selected page (step 1104). More specifically, the assignmentmanagement program 113 changes the value of the real page 402corresponding to the selected page to the invalid value.

Then, the assignment management program 113 determines whether or notthe selected page is the last page within the selected virtual volume201 (step 1105).

If it is determined at the step 1105 that the selected page is not thelast page within the selected virtual volume 201, the process returns tothe step 1102. At the step 1102, one of the unselected pages (e.g., thenext page to the previously selected page) is selected.

If it is determined at the step 1105 that the selected page is the lastpage within the selected virtual volume 201, the assignment of thephysical storage area to all the pages in which the specific patterndata only is stored among the pages within the selected virtual volume201 is canceled. In this case, the assignment management program 113releases the resource lock (step 1106), and ends the page discardprocess.

If it is determined at the step 1103 that the value of the discard mark403 corresponding to the selected page is invalid, the physical storagearea is not assigned to the selected page, the data other than thespecific pattern data is included in the selected page, or there is ahigh possibility that data other than the specific pattern data iswritten into the selected page. It is not permitted to cancel theassignment of the physical storage area to such page. Therefore, theassignment management program 113 does not perform the step 1104 andperforms the step 1105.

With the above, the explanation of the page discard process is ended.

Herein, referring to FIGS. 3 and 4, a specific example of the processesas shown in FIGS. 8 to 11 will be described below.

If the virtual volume 201A is selected at the step 802, the assignmentmanagement program 113 sets the valid value to the discard mark 403corresponding to the page to which the physical storage area is notassigned among all the pages within the virtual volume 201A (step 901).For example, when the values of the virtual page 401 corresponding tothe page 301A and the page 301B are “0x0000” and “0x5000”, the physicalstorage area is assigned to the page 301A, but not assigned to the page301B (see FIG. 4). In this case, the assignment management program 113sets the valid value (e.g., “1”) to the discard mark 403 correspondingto “0x0000” and sets the invalid value (e.g., “0”) to the discard mark403 corresponding to “0x5000”.

If the page 301A is selected at the step 902, the assignment managementprogram 113 sequentially copies the slots of the page 301A to the memory(step 904), and makes the comparison with the specific pattern data(step 905).

If the data of all the slots within the page 301A is matched with thespecific pattern data, the value of the discard mark 403 correspondingto the page 301A is kept as the valid value, and the next page 301B isselected (step 902). On the other hand, if at least one slot includingthe different data from the specific pattern data exists within the page301A, the value of the discard mark 403 corresponding to the page 301Ais changed to the invalid value (step 906), and the next page 301B isselected (step 902).

The same process as above is performed for the remaining pages of thevirtual volume 201A. However, since a page such as the page 301B towhich the physical storage area is not assigned is determined as “No” atthe step 903, the above comparison is not performed.

For example, even though the value of the discard mark 403 correspondingto the page 301A is kept as the valid value as a result of comparison atthe step 905, the value of the discard mark 403 corresponding to thepage 301A is changed to the invalid value when the data I/O for the page301A is subsequently performed (steps 909 and 910).

If the page discard determination process for all the pages of thevirtual volume 201A is ended, the page discard process for the virtualvolume 201A is performed. For example, if the value of the discard mark403 corresponding to the page 301A identified by the value “0x0000” ofthe virtual volume 401 is the valid value “1”, the value “0x0000” of thereal page 402 corresponding to the page 301A is changed to the invalidvalue (steps 1103 and 1104), as shown in FIG. 4. Thereby, the assignmentof the physical storage area to the page 301A is canceled.

Similarly, if the value of the real page 402 is changed to the invalidvalue for all the pages in which the value of the discard mark 403 isthe valid value, the page discard process is ended.

Essentially, it is not required that the specific pattern data is storedin the virtual volume 201, as described above. In other words, it is notrequired that the physical storage area is assigned to the page of thevirtual volume 201 to store the specific pattern data. However, therewere conventionally some cases where the physical storage area wasassigned to the page of the virtual volume 201 to store the specificpattern data, and there was no way for canceling the assignment.Therefore, the physical storage area could not be effectively used insome cases.

On the contrary, in the first embodiment of the invention, the specificpattern data is once stored in the virtual volume 201. That is, thephysical storage area is once assigned to the page of the virtual volume201 to store the specific pattern data. Thereafter, the comparison ismade between the data stored in the virtual volume 201 and the specificpattern data, and the assignment of the physical storage area to thepage in which the specific pattern data only is stored is canceled expost facto. The physical storage area in which the assignment iscanceled can be newly assigned to another page. Therefore, the physicalstorage area can be effectively used.

A second embodiment of the invention will be described below in detailusing the drawings.

In the first embodiment of the invention, the physical storage area isonce assigned to the page of the virtual volume 201 to store thespecific pattern data and then the assignment of the invention iscanceled. On the contrary, the write of the specific pattern data intothe virtual volume 201 is prevented in the second embodiment of theinvention.

The hardware configuration and the basic logical configuration accordingto the second embodiment of the invention are the same as in the firstembodiment. That is, FIGS. 1 to 5, FIG. 7 and FIG. 10 are alsoapplicable to the second embodiment. In the following, the differentpoints of the second embodiment from the first embodiment will bedescribed below.

FIG. 12 is a flowchart showing a data write process according to thesecond embodiment of the invention.

More specifically, FIG. 12 shows the process to be performed when theI/O control program 112 receives a data write request with the virtualvolume 201 designated as the write target.

At first, the I/O control program 112 receives a data write request(step 1201). This data write request includes the data to be written andthe information designating the address of the write target of the data.

The following explanation is concerned with the process performed by theI/O control program 112 in receiving the data of one page at the step1201. If the data of plural pages is received, the following process isrepeatedly performed. If the data of less than one page is received, theprocess as shown in FIG. 6 is performed as in the first embodiment.

Next, the I/O control program 112 determines whether or not the physicalstorage area is assigned to the page including the address of the writetarget (step 1202). More specifically, the I/O control program 112determines whether or not the effective value (i.e., the address of anypage in the pool volume 203) is registered in the real page 402corresponding to the page including the address of the write target byreferring to the assignment management table 114.

If it is determined at the step 1202 that the null value is registeredin the real page 402 corresponding to the page including the address ofthe write target, the physical storage area is not assigned to the pageincluding the address of the write target. In this case, the I/O controlprogram 112 stages the data of one slot among the data to be written(step 1203). This process is performed in the same way as the step 904in FIG. 9.

Next, the I/O control program 112 compares the staged data and thespecific pattern data, and determines whether or not they are matched(step 1204). This comparison may be made in the same way as the step 905in FIG. 9.

If it is determined at the step 1204 that the data of one slot and thespecific pattern data are unmatched, the data of one page received atthe step 1201 includes the different data from the specific patterndata. In this case, the I/O control program 112 assigns the physicalstorage area to the page corresponding to the address designated as thewrite target (step 1206). This assignment is performed in the same wayas the step 603 in FIG. 6.

Next, the I/O control program 112 writes the data at the addressdesignated as the write target (step 1207). This write is performed inthe same way as at the step 604 in FIG. 6. If the write at the step 1207is ended, the I/O control program 112 ends the data write process.

If it is determined at the step 1204 that the data of one slot and thespecific pattern data are matched, the I/O control program 112determines whether or not the data staged at the step 1203 correspondsto the last slot of the data of one page received at the step 1201 (step1205).

If it is determined at the step 1204 that the data of one slot and thespecific pattern data are matched, the process returns to the step 1203.At the step 1203, the I/O control program 112 stages the datacorresponding to the slot of slot staged immediately after and performsa process of the step 1204 and after.

If it is determined at the step 1205 that the staged data corresponds tothe last slot, the data of one page received at the step 1201 includesonly the same data as the specific pattern data. In this case, the I/Ocontrol program 112 ends the data write process without performing theassignment of the physical storage area to the page corresponding to theaddress designated as the write target and making the write of the datainto that page.

The process from the step 1203 to the step 1206 may be performed by theassignment management program 113 receiving an instruction from the I/Ocontrol program 112.

The I/O control program 112 of this embodiment may have a function ofperforming not only the data write process as shown in FIG. 12 but alsothe data write process as shown in FIG. 6. In this case, for example,the I/O control program 112 can switch the data write processes to beperformed in accordance with an instruction from the manager or user.

The above data write process has been described in an instance ofhandling the data write request sent from the host computer 130.However, when the copy of data is performed in the copy pair (i.e.,writing the data into the virtual volume 201 of the copy target) andwhen the restore of data is performed from the tape storage medium(i.e., writing the data read from the tape storage medium into thevirtual volume 201), the same process is performed.

In any case, since the write of the specific pattern data into thevirtual volume 201 is prevented, the physical storage area can beeffectively used.

When the copy of data in the copy pair is performed, it is also possibleto prevent the write of the specific pattern data by controlling thesending of data from the copy source, not by controlling the write ofdata into the copy target as above. In the following, the process ineach case will be described below.

FIG. 13 is a flowchart showing a first example of data copy between thelogical volumes according to the second embodiment of the invention.

For example, in the copy pair over two storage systems 100, when thecopy of data from the real volume 202 to the virtual volume 201 isperformed, the I/O control program 112 for the storage system 100comprising the real volume 202 of the copy source reads the data fromthe real volume 202 of the copy source (step 1301), and sends the readdata to the storage system 100 comprising the virtual volume 201 of thecopy target (step 1302).

The I/O control program 112 for the storage system 100 receiving thedata sent at the step 1302 performs the data write process as shown inFIG. 12 (step 1303). Thereby, the write of the specific pattern datainto the virtual volume 201 of the copy target is prevented.

FIG. 14 is a flowchart showing a second example of data copy between thelogical volumes according to the second embodiment of the invention.

An instance of performing the copy of data from the real volume 202 tothe virtual volume 201 in the same way as in FIG. 13 will be describedbelow. Herein, the copy of all the data stored in the real volume 202 tothe virtual volume 201 is performed.

The I/O control program 112 for the storage system 100 comprising thereal volume 202 of the copy source reads the data of one page from thereal volume 202 of the copy source (step 1401).

Then, the I/O control program 112 stages the data of one slot among theread data of one page (step 1402). This process is performed in the sameway as at the step 904 in FIG. 9.

Next, the I/O control program 112 compares the staged data and thespecific pattern data and determines whether or not they are matched(step 1403). This comparison is performed in the same way as at the step905 in FIG. 9.

If it is determined at the step 1403 that the data of one slot and thespecific pattern data are unmatched, the data of one page read at thestep 1401 includes different data from the specific pattern data. Inthis case, the I/O control program 112 sends the data of one page readat the step 1401 to the storage system 100 comprising the virtual volume201 of the copy target (step 1404).

If it is determined at the step 1403 that the data of one slot and thespecific pattern data are matched, the I/O control program 112determines whether or not the data staged at the step 1402 correspondsto the last slot of the data of one page read at the step 1401 (step1405).

If it is determined at the step 1405 that the staged data does notcorrespond to the last slot, the process returns to the step 1402. Atthe step 1402, the I/O control program 112 stages the data correspondingto the next slot of the previously staged slot, and performs the processof the step 1403 and following.

If it is determined at the step 1405 that the staged data corresponds tothe last slot, the data of one page read at the step 1401 includes onlythe same data as the specific pattern data. In this case, the I/Ocontrol program 112 does not send the data of one page read at the step1401 to the storage system 100 comprising the virtual volume 201 of thecopy target, and performs the step 1406.

The I/O control program 112 determines at the step 1406 whether or notthe data of one page read at the step 1401 is the last page in the realvolume 202 of the copy source.

If it is determined at the step 1406 that the read data is not the lastpage, the process returns to the step 1401. At the step 1401, the I/Ocontrol program 112 reads the data of the next page of the previouslyread page, and performs the process following the step 1402.

The I/O control program 112 for the storage system receiving the datasent at the step 1404 performs the data write process as shown in FIG. 6to write the received data into the virtual volume 201 of the copytarget (step 1411).

Since the page including only the same data as the specific pattern datais not sent at the step 1404, the physical storage area is not assignedto the page including only the same data as the specific pattern data atthe step 1411.

Though the copy of data in the copy pair over the two storage systems100 is shown in FIGS. 13 and 14, the same process may be performed inthe case of the copy pair within one storage system 100 (i.e., the realvolume 202 of the copy source and the virtual volume 201 of the copytarget are stored in the same storage system 100).

The process as shown in FIG. 14 may be performed in the storage system100 of the first embodiment. When the process as shown in FIG. 14 isperformed in the storage system 100 of the first embodiment, theassignment of the physical storage area for the copy between the logicalvolumes is controlled through the process of FIG. 14, and the assignmentof the physical storage area for other processes (e.g., writing the dataread from the tape storage medium) is controlled through the pool JOB(see FIG. 8 and so on).

With the second embodiment of the invention as described above, theassignment of the physical storage area to the page including only thesame data as the specific pattern data is prevented. Therefore, thephysical storage area can be effectively used.

Though the data including the consecutive “0” only is employed as oneexample of the specific pattern data in the first and secondembodiments, the specific pattern data may be arbitrary. To make moreeffective use of the physical storage area, it is desirable that thespecific pattern data is selected to have the more physical storage areaunassigned to the page of the virtual volume 201. More specifically, itis desirable that the data of the highest occurrence frequency patternamong the data written in accordance with the write request for thevirtual volume 201 is selected as the specific pattern data.

For example, if the physical storage area is assigned to all the pagesof the virtual volume 201, the assignment management program 113 mayread all the data stored in the virtual volume 201 and specify the dataof the highest occurrence frequency pattern before the pool JOB (FIGS. 8to 11) for the virtual volume 201 is performed. In this case, the dataof the highest occurrence frequency pattern is selected as the specificpattern data.

The assignment management program 113 stores the selected specificpattern data in the predetermined address range 303 of the pool volume203 associated with the virtual volume 201.

Or when the data is copied as shown in FIGS. 13 and 14, the assignmentmanagement program 113 for the storage system 100 comprising the realvolume 202 of the copy source may read all the data of the real volume202 of the copy source and specify the data of the highest occurrencefrequency pattern. In this case, the data of the highest occurrencefrequency pattern is selected as the specific pattern data.

The I/O control program 112 of the storage system 100 including the realvolume 202 of the copy source previously may send the data of theselected specific pattern to the storage system including the virtualvolume 201 of the copy source.

In this way, the physical storage area can be used more effectively byusing the data of the highest occurrence frequency pattern as thespecific pattern data.

In the above way, the first and second embodiments of the invention aimto use the physical storage area effectively. For this purpose, in thefirst embodiment, after the physical storage area is once assigned tothe page storing only the specific pattern data, the assignment iscanceled. On the other hand, in the second embodiment, the data writeprocess or data send process is controlled so that the physical storagearea may not be assigned to the page storing only the specific patterndata from the first. In this way, the first and second embodiments havethe common technical significance.

What is claimed is:
 1. A storage system for storing the data written bya host computer, the storage system comprising a storage mediumincluding a plurality of physical storage areas, and a controller forcontrolling the write of the data into the storage medium and the readof the data from the storage medium, wherein the controller controls thehost computer to recognize a first logical volume; a storage area spaceof the first logical volume includes a plurality of address ranges; andthe controller holds information for managing the assignment of the eachphysical storage area to the each address range; determines whether ornot the physical storage area is assigned to the address range specifiedby a received data write request, if the data write request for any ofthe address ranges of the first logical volume is received; assigns thephysical storage area not yet assigned to any of the address ranges tothe specified address range if the physical storage area is not assignedto the specified address range; writes the write requested data on thedata write request into the physical storage area assigned to thespecified address range; reads the data from the physical storage areaassigned to the address range of the first logical volume if apredetermined condition is satisfied; determines whether or not the readdata includes the data of a predetermined pattern only; cancels theassignment of the physical storage area to the address range if the readdata includes the data of the predetermined pattern only; determineswhether or not the physical storage area is assigned to the addressrange specified by a data read request if the data read request for anyof the address ranges of the first logical volume is received; sends theread data to a sender of the data read request by reading the data fromthe physical storage area assigned to the specified address range if thephysical storage area is assigned to the specified address range; andsends the data of the predetermined pattern to the sender of the dataread request if the physical storage area is not assigned to thespecified address range.